The present invention relates to computerized static converter control in general, and more particularly to inverter control in an adjustable frequency AC motor drive.
It is known to implement digital control of the thyristors of an AC motor drive with the aid of a computer. See for instance U.S. Pat. No. 4,427,933. As disclosed in the patent, for inverter gating a down-counter is preset at a computed time interval count and is allowed to count from such count down to zero, at which time firing is instantly triggered.
The purpose of the present invention is to eliminate a time lag, existing with the prior art approach, which prevents an immediate adjustment of the anticipated firing instant in order to match the new reference as the frequency reference changes. The invention is applicable to a simplified circuit, that is, it operates in the context of a system which must remain simple while overcoming the problem caused by the time lag.